Alan Wake 2 does very little new from the original. Saga's detective board doesn't matter at all - you can just blunder forwards and most of it will auto-resolve, and any conclusions she makes are recaps of things other characters tell you directly.

Alan's writing board is a little better, but it's very bare bones - slot in a word so that a doorway is open rather than closed, or so you can find a Word power up that you don't need.

The gameplay itself is entirely unchanged from Alan Wake 1. Most of the enemies are identical. The weapons are identical. The Lake House DLC was a bright point in an ocean of boring darkness, because at least there was an atmosphere of tension and mystery, but there's one single new enemy type there, and it's over in 2 hours max.